In many parts of the world due to inadequate rainfall it is necessary at certain times during the year to artificially water turf and landscaping. An ideal irrigation system for turf and landscaping should utilize a minimum number of valves, supply lines and sprinklers. Preferably the valves should be turned ON and OFF by an inexpensive, yet reliable electronic irrigation controller that is easy to program and can carry out a wide variety of watering schedules. The goal is to uniformly distribute the optimum amount of water over a given area. The type, placement and flow rates for each of the sprinklers are pre-selected when an irrigation system is designed and/or installed. The optimum flow rate provided by each sprinkler should preferably fall within plus or minus one-quarter gallon-per minute (GPM). The amount of water supplied by each sprinkler is largely determined by the size and configuration of its nozzle orifice(s), although variations result from fluctuations in water pressure that cannot be fully negated with regulators.
Residential and commercial irrigation systems typically include one or more solenoid operated valves that are turned ON and OFF by an electronic irrigation controller. The valves admit water to various subterranean branch lines usually made of PVC pipe that typically have several sprinklers connected to risers coupled to the branch lines at spaced intervals. Each combination of a solenoid valve and its associated sprinklers is referred to in the irrigation industry as a station or zone. A modern electronic irrigation controller typically includes a microprocessor that executes one or more watering programs. The watering programs can be pre-programmed by the user via push button and/or rotary controls. The controller usually has an LCD or other display to facilitate programming by the user. Often the controller will revert to a default watering program in the case of a power failure. The microprocessor controls the solenoid valves via suitable drivers and switching devices. The valves are opened and closed by the microprocessor in accordance with the pre-programmed run and cycle times for each of the stations.
Over the past decade, modular expandable irrigation controllers have gained increasing popularity. In these controllers, the base portion of the system contains the microprocessor and user actuated controls. Each station is then controlled by a corresponding station module which comprises a plastic housing that encloses and supports a station module circuit, as well as wire connection terminals for connecting wires to a plurality of solenoid actuated valves. Typically each station module circuit includes a plurality of triacs or other switching devices and can independently control a plurality of solenoid actuated valves, i.e., stations. The station modules contain pins, sockets, card edge connectors or some other standard form of electromechanical connectors for allowing them to be inserted into slots or receptacles in either the housing that contains the microprocessor or a separate back panel hinged to the microprocessor housing. When the station modules are plugged into a modular expandable irrigation controller they are mechanically supported and an electrical connection is made between the microprocessor and the driver. See for example, U.S. Pat. No. 6,721,630 B1 of Peter Woytowitz, assigned to Hunter Industries, Inc., the assignee of the present application.
The advantage of an irrigation controller with a modular expandable configuration is that the controller need only be equipped with the minimum number of station modules that can control the total number of stations needed. Thus, for example, an irrigation system may have only three zones, requiring only a single station module, while another may have twelve stations which might require four station modules. Considerable cost savings are thus achieved. Moreover, if an irrigation system expands after initial installation because the landscaping has increased, additional station modules can be plugged into the controller. The station modules can also be removed and replaced if damaged, for example, during a lightening strike. In some modular expandable irrigation systems the base unit is capable of controlling a minimal number of stations without requiring the addition of any station modules. In others, such as the ICC™ irrigation controller manufactured and sold by Hunter Industries, Inc., at least a power module and one irrigation station module must be plugged into the controller in order to operate any stations or zones.
A modular expandable irrigation controller requires a dedicated field valve line to extend from the controller to the solenoid valve of each station. A common line returns from each of the solenoids to complete the circuit. Thus each station is controlled by the microprocessor through a separate circuit. When a residential irrigation system is installed, typically the controller is mounted in the garage and all the wires are laid underground to one or more subterranean valve boxes that contain the solenoid operated valves. The installers frequently do not have the foresight to install extra wires to support additional stations at some future date. This can lead to major cost and expense if the homeowner has a modular expandable irrigation controller that allows for the addition of more stations, but the hard wires to reach them are not already in place.
Another type of irrigation controller exists that does not require a dedicated field valve line to each station. So-called “decoder” systems are available in either two wire or three wire versions. In a two-wire decoder system one or two way communication between the microprocessor and the valves is achieved by encoding signals and transmitting them over the same two wires that carry the power to the valve solenoids. The valves are connected in parallel to the two wires through decoder circuits that are used to identify commands uniquely intended for that station. In a three-wire decoder system two of the wires are used for power and the third is used for communications. See, for example, U.S. Pat. No. 3,653,595 of Greengard, Jr. et al.; U.S. Pat. No. 4,209,131 of Barash et al. assigned to Motorola; U.S. Pat. No. 4,176,395 of Evelyn-Veere et al. assigned to Clemar Manufacturing; and U.S. Pat. No. 5,048,755 of Dodds et al.
In irrigation control systems of the decoder type signal modulation (AM or FM) is typically used to encode the commands and data sent between the microprocessor and the stations. Decoder systems can easily be expanded to provide additional stations simply by attaching additional decoder circuits and valves to the two-wire or three-wire path at the locations of each new station. It is not necessary to run dedicated field valve lines all the way back to the main controller for each new station. Thousands of feet of wiring can be accommodated by decoder irrigation systems so very large properties such as golf courses, housing subdivisions, apartments and condominiums can easily be automatically irrigated. Despite all their apparent versatility and attractiveness, decoder irrigation systems are much more complex, less well understood by users, and harder to troubleshoot than conventional modular expandable irrigation control systems that utilize a dedicated field valve line for each station.
U.S. Pat. No. 5,389,658 of Sarver discloses a method of retrofitting an existing irrigation control system including a centralized controller, a plurality of independent valve control lines extending between the controller and the valves, and a return line extending from each of the valves to the controller. A terminal strip is installed within the controller and connects each of the valve control lines together. A signal encoder circuit board is permanently installed within the controller and a decoder is installed in series with each valve assembly. When the retrofitting is complete the irrigation control system of the Sarver patent essentially comprises a two wire decoder system. The first “wire” is the combination of each of the valve control lines now all in parallel to each other and all connected to one another via the terminal strip. The “second wire” is the common return line returning from each valve assembly. The permanent conversion of a conventional irrigation controller to a decoder system is not a practical solution for landscape contractors because it requires too much expertise and effort to make the physical modifications that are required. In addition, few conventional irrigation controllers have the space and other physical configuration requirements that would allow them to accept the installation and connection of the terminal strip and signal encoder circuit board. Moreover, such a retrofitting process would be impractical given the wide variety of programming and output formats of various conventional controllers already installed in the field. The resulting decoder controller disclosed in Sarver does not afford the benefits of a simpler conventional irrigation control system wherein each station essentially comprises a separate circuit.